1. Field of the Invention
The present invention relates to a current-driven pixel circuit which controls a current for an organic electroluminescence (hereinafter simply referred to as “EL”) element using a current data signal.
2. Description of the Related Art
Conventionally, a current-driven pixel circuit is known as a pixel circuit for driving an organic EL element. In the current-driven pixel circuit, a gate voltage of a driver transistor is set based on a current data signal while a corresponding current is applied to the driver transistor.
When a data voltage is simply set on the gate of the driver transistor, the drive current flowing through the driver transistor varies because of a variation in the threshold voltage among the driver transistors, resulting in a variation in light emission brightness of the organic EL element. With a current-driven pixel circuit, because the gate voltage of the driver transistor is set while a current corresponding to the current data signal is supplied through the driver transistor, it is possible to obtain relatively accurate drive current (see Japanese Patent Laid-Open Publication No. 2001-147659).
In a current-driven pixel circuit, in order to realize a minimum brightness, a voltage corresponding to a small data current signal must be set on the gate of the driver transistor, and therefore, there is a problem in that the time before setting becomes long.
Alternatively, there is another proposed method to drive the organic EL element with a contracted drive current by using a relatively large current data signal and setting a voltage corresponding to the current data signal on the gate of the driver transistor (see Japanese Patent Laid-Open Publication No. 2004-12897). In this method, however, it is not possible to apply a voltage corresponding to each driver transistor when the voltage is contracted and a constant voltage is applied. Therefore, there is a problem in that the error becomes large when the electron mobility varies among driver transistors.